1. Field of the Invention
The present invention relates to a vibrating gyroscope and, more particularly, to a vibrating gyroscope that is applied to a navigation system which detects a position of a mobile by detecting its rotational angular velocity and guides it properly, a system for damping a vibration such a device for protecting an unsteady hold which detects an external vibration and damps it properly, or the like.
2. Description of the Prior Art
FIG. 19 is a circuit diagram showing a prior art of a vibrating gyroscope. The vibrating gyroscope 1 includes a piezoelectric vibrator 2.
The piezoelectric vibrator 2 includes a regular triangular prism-shaped vibrating body 3, three piezoelectric elements 4a, 4b and 4c are formed on centers of three side faces of the vibrating body 3, respectively. In the piezoelectric vibrator 2, when similar driving signals are applied to, for example, the two piezoelectric elements 4a and 4b, the vibrating body 3 bends and vibrates in a direction perpendicular to a main surface of the piezoelectric element 4c. In this state, similar detecting signals are obtained from the piezoelectric elements 4a and 4b. Then, in this state, when a rotational angular velocity is applied to the piezoelectric vibrator 2 about an axis of the vibrating body 3, the bending and vibrating direction of the vibrating body 3 is changed by a Coriolis force, detecting signals responsive to the rotational angular velocity are obtained from the two piezoelectric elements 4a and 4b. In this case, for example, a voltage of one detecting signal from the piezoelectric element 4a becomes larger and a voltage of the other detecting signal from the piezoelectric element 4b becomes smaller responsive to the rotational angular velocity.
Thus, the piezoelectric element 4c of the piezoelectric vibrator 2 is connected to an input terminal of an oscillation circuit 5 consisting of, for example, an amplifier. An output terminal of the oscillation circuit 5 is connected to ends of two resistors 6a and 6b, the other ends of the resistors 6a and 6b are connected to the two piezoelectric elements 4a and 4b, respectively. The piezoelectric elements 4a and 4b are connected to a non-inverting input terminal and an inverting input terminal of a differential amplifier circuit 7, respectively.
Accordingly, in the vibrating gyroscope 1, by an output signal from the differential amplifier circuit 7, it can be detected that any rotational angular velocity is not applied, or an applied rotational angular velocity can be detected.
However, in the vibrating gyroscope 1, since the resistor 6a and the piezoelectric element 4a are connected in series and the resistor 6b and the piezoelectric element 4b are connected in series as shown in FIG. 20, when a resonance characteristic of the piezoelectric vibrator 2 is shifted and each impedance of the piezoelectric elements 4a and 4b is changed and is different from each other by changing an atmospheric temperature or environment, phases of driving signals L and R applied to the piezoelectric elements 4a and 4b are different from each other, for example, as L=Vsin(x+5) and R=Vsin(x-5) shown in FIG. 21.
Since the driving signals L and R are applied to the non-inverting input terminal and the inverting input terminal of the differential amplifier circuit 7, when any rotational angular velocity is not applied to the vibrating gyroscope 1 in particular, as shown in FIG. 21, the output signal L-R which is not zero is obtained from the output terminal of the differential amplifier circuit 7, that is, an offset change (a drift) is generated. Thus, there is a problem it is not detected by the output signal from the differential amplifier circuit 7 that any rotational angular velocity is not applied to the vibrating gyroscope 1.
In order to solve the above problem, there is a method for correcting the output signal from the differential amplifier circuit by using a circuit for treating a signal or a circuit having a learning function. However, in the method, a circuit becomes a large scale and a complex structure, and it is not enough for a good characteristic since it is necessary that a circuit is adjusted to a special condition. Because, it fails to discriminate between a change of a signal generated by changing the resonance characteristic of the vibrator and a change of a signal generated by changing the applied rotational angular velocity, and it fails to discriminate a shift of the resonance characteristic not having any directional characteristic.